DE102021003844A1 - On-board network for a motor vehicle - Google Patents

Abstract

The invention relates to an on-board network (1) for a motor vehicle, comprising at least one HV battery (2) for providing a positive potential (H+) and a negative potential (H-) and at least one HV consumer (3, 4), wherein an insulation monitor (5) for monitoring insulation resistances (R _{iso_P} , R _{iso_N} ) to a vehicle ground (PA) that is galvanically isolated from the vehicle electrical system (1) is provided, with between the positive potential (H+) and the vehicle ground (PA) and between the negative Potential (H-) and the vehicle ground (PA) each have a Y-capacitance (C _{Y_P} , C _{Y_N} ) provided, with a voltage center tap (6) present in the vehicle electrical system (1) or in a component of the vehicle electrical system (1) between the positive potential (H+) and the negative potential (H-) is connected to the vehicle ground (PA) by means of an ohmic coupling resistor (R _K ).

Description

The invention relates to an electrical system for a motor vehicle according to the preamble of claim 1.

Out of DE 10 2019 202 892 A1 discloses an on-board power supply system for a motor vehicle, the on-board power supply system having a high-voltage energy store for providing a first high-voltage potential and a second high-voltage potential that is different from the first, so that a total voltage can be tapped between the first and the second high-voltage potential. Furthermore, the vehicle electrical system arrangement has a first insulation resistance between the first high-voltage potential and a predetermined electrical ground and a second insulation resistance between the second high-voltage potential and the predetermined electrical ground and an insulation monitoring device that is designed to monitor the first and second insulation resistance . The HV (high-voltage) electrical system of a vehicle with an electric drive typically consists of at least one HV battery with battery contactors and HV consumers, for example a pulse-controlled inverter. As a rule, the high-voltage vehicle electrical system is implemented as an IT (Isole Terre) network and is therefore completely electrically isolated from the vehicle ground. However, parasitic resistances in the cables, HV consumers, the battery and so on result in a high-impedance connection between the positive or negative high-voltage potential and the vehicle ground, the so-called insulation resistance, or the above-mentioned respective first and second insulation resistance. As long as this resistance has a high resistance, i.e. in the megaohm range, there is no danger. For safety reasons, this insulation resistance is permanently monitored using an insulation monitoring device, also known as an insulation monitor. If a defined threshold value is not reached, a warning can be generated and, depending on the operating state, the HV vehicle electrical system can be disconnected from the battery via the battery contactors and a safe state can be established. In addition to the insulation resistance, there are capacitances in every HV vehicle electrical system, in particular what are known as ground capacitances, which lie between the HV connections and the vehicle ground. These result from parasitic effects, for example caused by cable shields, and are even deliberately built in to improve EMC (electromagnetic compatibility) behavior. According to the formula E=½×C×U ² , energy E is stored in these capacitors with capacitance C when a voltage U is present. If a person then touches a high-voltage contact and the vehicle ground at the same time, these capacitors are discharged or recharged via the body and could in principle, ie if these currents were too high, lead to a hazard. In order to keep the hazard potential low, there are limit values for the maximum permitted stored, or rather effective energy in the capacitors in various standards. This directly results in a limitation of the maximum permissible total capacity depending on the HV total voltage. In addition, for safety reasons, the worst case must be assumed, and a maximally asymmetrical HV vehicle electrical system must be assumed, which is the case when the voltage of one HV pole measured against earth almost corresponds to the entire HV voltage. This can occur, among other things, due to dirt resistance or leakage currents over the service life. Due to the limitation of the maximum permissible total capacity described above, there is no potential hazard even with an asymmetrical vehicle electrical system, i.e. if the voltages between the positive high-voltage potential and ground and between the negative high-voltage potential and ground are different. In addition to the disadvantage of limiting the maximum permissible total capacity, it can also happen in this case, i.e. with an asymmetrical vehicle electrical system, that when the vehicle is connected to a charging station, for example via the DC charging interface, the positive or negative voltage potential with respect to earth of the charging station and vehicle is different. When the charging station is switched on, this can lead to undesired, undefined compensation processes, which in the worst case can prevent charging.

The invention is based on the object of specifying an improved vehicle electrical system for a motor vehicle, in particular for an electrically driven motor vehicle.

The object is achieved according to the invention by an electrical system for a motor vehicle according to claim 1.

Advantageous configurations of the invention are the subject matter of the dependent claims.

A vehicle electrical system according to the invention for a motor vehicle comprises at least one HV battery for providing a positive potential and a negative potential and at least one HV consumer, with an insulation monitor for monitoring insulation resistances to a vehicle ground that is galvanically isolated from the vehicle electrical system, with between the positive potential and the vehicle mass as well as between the negative potential and the vehicle mass in each case a Y-capacitance is provided. According to the invention, there is one in the vehicle electrical system or in a component of the vehicle electrical system Center voltage tap between the positive potential and the negative potential connected to the vehicle ground by means of an ohmic coupling resistor. The insulation monitor can be designed, for example, as a resistance insulation monitor.

Due to the solution according to the invention, the deviation of the distribution of the potentials from a symmetrical distribution is very small. Thus the energy content/charge stored in the Y-capacitors is always very close to the minimum achievable. As a result, a larger Y-capacity can be permitted in the vehicle electrical system, while still meeting the legal requirements with regard to the stored energy/charge. A cheaper and/or better EMC filtering in the components of the high-voltage vehicle electrical system is therefore possible.

In one embodiment, the voltage center tap lies between two resistors connected as a voltage divider or is formed by a capacitive voltage divider.

In one embodiment, the resistances of the voltage divider are in the form of HV loads connected in series or as internal resistances of at least two HV batteries connected in series.

In one embodiment, the resistances of the voltage divider are significantly smaller compared to the coupling resistance and measuring resistances of the insulation monitor, which is designed as a resistance insulation monitor.

In one embodiment, the measuring resistors and the coupling resistor are in the range of more than 100 kOhm.

In one embodiment, the coupling resistor includes a fixed resistor and/or a variable resistor.

In one embodiment, the coupling resistor is designed as a series circuit made up of the fixed resistor and the variable resistor.

• - eine Reihenschaltung von HV-Spannungsversorgungen für ein Controlboard,
• - eine Reihenschaltung von Halbbrücken und/oder H-Brücken,
• - eine Multilevel-Halbbrücke,
• - eine Reihenschaltung von Invertern,
• - ein Multilevel-Inverter,
• - eine Heizschaltung mit Reihenschaltungen von zwei oder mehreren Heizelementen,
• - ein Abgriff eines Verbindungspunkts von Batterie-Modul-Reihenschaltungen.

In one embodiment, at least one from the following list is coupled to the vehicle ground via the coupling resistor:

• - a series connection of HV power supplies for a control board,
• - a series connection of half-bridges and/or H-bridges,
• - a multilevel half bridge,
• - a series connection of inverters,
• - a multilevel inverter,
• - a heating circuit with series connections of two or more heating elements,
• - a tap of a connection point of battery module series circuits.

The vehicle electrical system can be part of a motor vehicle, in particular an electrically powered motor vehicle.

If the coupling resistor is designed as a series connection of the fixed resistor and the variable resistor, a high variable resistance can be set when the vehicle is not connected to a DC charging station, while the vehicle is connected to a DC charging station is, a lower variable resistance is set.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

• 1 eine schematische Ansicht eines Bordnetzes eines Kraftfahrzeugs,
• 2 eine schematische Ansicht einer Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 3 eine schematische Ansicht einer weiteren Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 4 eine schematische Ansicht einer weiteren Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 5 eine schematische Ansicht einer weiteren Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 6 eine schematische Ansicht einer weiteren Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 7 eine schematische Ansicht einer weiteren Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 8 eine schematische Ansicht eines Simulationsaufbaus einer Ausführungsform eines Bordnetzes eines Kraftfahrzeugs,
• 9 schematische Diagramme zur Darstellung von Simulationsergebnissen für eine Simulation ohne Koppelwiderstand, und
• 10 schematische Diagramme zur Darstellung von Simulationsergebnissen für eine Simulation mit einem Koppelwiderstand.

show:

• 1 a schematic view of a vehicle electrical system of a motor vehicle,
• 2 a schematic view of an embodiment of a vehicle electrical system of a motor vehicle,
• 3 a schematic view of a further embodiment of a vehicle electrical system of a motor vehicle,
• 4 a schematic view of a further embodiment of a vehicle electrical system of a motor vehicle,
• 5 a schematic view of a further embodiment of a vehicle electrical system of a motor vehicle,
• 6 a schematic view of a further embodiment of a vehicle electrical system of a motor vehicle,
• 7 a schematic view of a further embodiment of a vehicle electrical system of a motor vehicle,
• 8th a schematic view of a simulation setup of an embodiment of an on-board network of a motor vehicle,
• 9 schematic diagrams showing simulation results for a simulation without coupling resistance, and
• 10 schematic diagrams showing simulation results for a simulation with a coupling resistor.

Corresponding parts are provided with the same reference symbols in all figures.

1 is a schematic view of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle.

The vehicle electrical system 1 is, for example, an HV (high-voltage) vehicle electrical system and typically includes at least one HV battery 2 and HV consumers 3, 4. The vehicle electrical system 1 is usually electrically isolated from a vehicle ground PA. An insulation resistance R _{iso_P} , R _{iso_N} results between a positive potential H+ and the vehicle ground PA and between a negative potential H− and the vehicle ground PA as a result of parasitic effects. For safety reasons, an insulation monitor 5 is provided, which monitors the insulation resistances R _{iso_P} , R _{iso_N} . Furthermore, Y-capacitors C _{Y_P} , C _{Y_N} are provided between the positive potential H+ and the vehicle ground PA and between the negative potential H− and the vehicle ground PA.

Fluctuations in the vehicle electrical system 1, which are caused by the insulation monitor 5, which can be designed in particular as a resistance insulation monitor, can be reduced by a in the vehicle electrical system 1 or in a component of the vehicle electrical system 1, for example a HV consumer 3, 4 , the in 1 is symbolized by two load resistors R _VP and R _VN connected as a voltage divider, the existing voltage center tap 6 is used. This voltage center tap 6 is connected to vehicle ground PA via an ohmic coupling resistor R _K , which can include a fixed resistor R _F and/or a variable resistor Rv. In the embodiment shown, the coupling resistor R _K is designed as a series connection of a fixed resistor R _F and a variable resistor Rv.

In other embodiments, the voltage center tap 6 can also be formed by means of a capacitive voltage divider.

The influence of the insulation monitor 5 on the displacement of the potentials H+, H- in relation to the vehicle ground PA is reduced by the coupling of the voltage center tap 6 to the vehicle ground PA by means of the coupling resistor R _K . The function of the insulation monitor 5 when calculating the insulation value of the insulation resistances R _{iso_P} , R _{iso_N is} not disrupted, in particular if the value of the coupling resistance R _K does not change during the measurement period of the insulation monitor 5 . The energy content stored in the Y capacitances C _{Y_P} , C _{Y_N} of the vehicle electrical system 1 can be reduced due to the only slight shift in the potentials H+, H−. This is advantageous for improving the filtering of active, in particular clocking, HV components and for vehicles with higher DC system voltages, for example 800V. When coupling HV systems with different insulation designs, it is also possible to avoid overloading the insulation of the weaker HV system. For example, the insulation of a 500V charging station is protected by a galvanically coupled charging system when charging an 800V vehicle.

Due to the coupling resistor R _K , the insulation monitor 5 has a significantly shorter detection time, since charge reversal processes take place more quickly.

By using a series connection of a fixed resistor R _F with a variable resistor Rv, higher isolation can be allowed if the HV system has a lower Y capacitance C _{Y_P} , C _{Y_N} , for example if the vehicle is not connected to a DC charging station . If the Y capacitance C _{Y_P} , C _{Y_N} is higher, for example if the vehicle is connected to a DC charging station, the coupling resistance R _K can be reduced by its variable resistance Rv and the potential shift by the insulation monitor 5 is less.

• - Reihenschaltung von HV-Spannungsversorgungen für Controlboards,
• - Serienschaltungen von Halbbrücken und H-Brücken,
• - Multilevel-Halbbrücken,
• - Serienschaltungen von Invertern,
• - Multilevel-Inverter,
• - Heizschaltungen mit Reihenschaltungen von zwei oder mehreren Heizelementen,
• - Abgriffe von Verbindungspunkten von Batterie-Modul-Reihenschaltungen.

Examples for the possible use of an ohmic coupling of a voltage center tap 6 to the vehicle ground PA are:

• - Series connection of HV power supplies for control boards,
• - series circuits of half-bridges and H-bridges,
• - multilevel half bridges,
• - series connections of inverters,
• - multilevel inverter,
• - heating circuits with series connections of two or more heating elements,
• - Pick-offs from connection points of battery-module series circuits.

The impedances of series circuits of HV loads 3, 4 or HV sources are preferably significantly smaller in comparison to the coupling resistance R _K and to measuring resistances of the insulation monitor 5. Since the measuring resistors R _{mess_p} , R _{mess_n} and the coupling resistor R _K can be in the range of several 100kOhms or even in the MOhm range, the series connections of HV consumers 3, 4 or HV sources do not require a large power consumption in order to achieve a significant represent smaller impedance. In this respect, also auxiliary power supplies suitable for this use. In the case of HV sources, the source impedance and/or the internal resistance must be taken into account. This is normally in the mOhm range and thus also meets this requirement.

In the following figures, only a single coupling resistor R _K is shown instead of the series connection of a fixed resistor R _F and a variable resistor Rv. In any case, however, a series connection of a fixed resistor R _F and a variable resistor Rv can also be provided instead.

2 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 2 agrees with the embodiment according to 1 largely agree. However, the voltage center tap 6 is formed by means of a capacitive voltage divider from two capacitances C _{x_P} , C _{x_N} instead of consumer resistors.

In addition, the vehicle electrical system 1 is connected to a three-phase AC voltage connection 7 via a rectifier 8 with power factor correction (3-level PFC, for example a Vienna rectifier).

3 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 3 agrees with the embodiment according to 1 largely agree. However, the voltage center tap 6 is formed by means of a capacitive voltage divider from two capacitances C _{x_P} , C _{x_N} instead of consumer resistors.

In addition, the vehicle electrical system 1 with a DC charging station 9, which is shown with Y capacitances C _{y_P1} , C _{y_N1} , insulation resistances R _{iso_P1} , R _{iso_N1} , similar to the vehicle electrical system 1 and with an output capacitance C, via a 3-level DC Boost converter 11 connected in the vehicle, wherein the capacitive voltage divider from the two capacitances C _{x_P} , C _{x_N} in the 3-level DC boost converter 11 is arranged. Furthermore, the vehicle ground PA is connected to a ground PA′ in the DC charging station 9 via a ground cable 12 .

4 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 4 agrees with the embodiment according to 1 largely agree. However, the voltage center tap 6 is formed by means of a capacitive voltage divider from two capacitances C _{x_P} , C _{x_N} instead of consumer resistors.

In addition, the vehicle electrical system 1 is connected to a series connection of H-bridges 13, 14, for example LV-DCDC converters or isolated DCDC converters of an on-board charger.

5 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle.

The vehicle electrical system 1 includes two series-connected HV batteries 2.1, 2.2 or battery strings and an HV consumer 3. The vehicle electrical system 1 is electrically isolated from a vehicle ground PA. An insulation resistance R _{iso_P} , R _{iso_N} results between a positive potential H+ and the vehicle ground PA and between a negative potential H− and the vehicle ground PA as a result of parasitic effects. For safety reasons, an insulation monitor 5 is provided, which monitors the insulation resistances R _{iso_P} , R _{iso_N} . Furthermore, Y-capacitors C _{Y_P} , C _{Y_N} are provided between the positive potential H+ and the vehicle ground PA and between the negative potential H− and the vehicle ground PA. The HV consumer 3 is connected between the positive potential H+ and the negative potential H-.

Fluctuations in the vehicle electrical system 1, which are caused by the insulation monitor 5, which can be designed in particular as a resistance insulation monitor, can be reduced by a vehicle electrical system 1 or in a component of the vehicle electrical system 1, for example the HV batteries 2.1, 2.2 , in the 5 are connected in series and their internal resistances thus form a voltage divider, existing voltage center tap 6 is used. This voltage center tap 6 is connected to vehicle ground PA via an ohmic coupling resistor R _K , which can include a fixed resistor R _F and/or a variable resistor Rv.

6 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 6 agrees with the embodiment according to 1 largely agree. However, the voltage center tap 6 is formed by means of a capacitive voltage divider from two capacitances C _{x_P} , C _{x_N} instead of consumer resistors.

In addition, the vehicle electrical system 1 is connected to a 3-level inverter 15 for an electrical machine 16 . The 3-level inverter 15 can be designed, for example, as a 3-level NPC inverter, a T-type inverter or a flying inverter.

7 is a schematic view of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 7 agrees with the embodiment according to 1 largely agree. However, the voltage center tap 6 is formed by means of a capacitive voltage divider from two capacitances C _{x_P} , C _{x_N} instead of consumer resistors.

In addition, the vehicle electrical system 1 is connected to a series connection of two B& bridge inverters 17 for two electrical machines 16 .

8th is a schematic view of a simulation setup of an embodiment of an on-board network 1 of a motor vehicle, for example an electrically powered motor vehicle. The embodiment according to 8th agrees with the embodiment according to 1 largely agree. Furthermore, two measurement resistors R _{mess_p} , R _{mess_n} of the insulation monitor 5 are arranged between the positive potential H+ and the vehicle ground PA and between the negative potential H− and the vehicle ground PA by respective switches S1, S2. Line resistances R _L are also shown in series with the Y capacitances C _{Y_P} , C _{Y_N} , which are unavoidably present in real components and therefore have to be taken into account in the simulation, albeit only with a very low resistance value of 0.01 ohms, for example.

• R_{iso_p} = 10⁸ Ohm
• R_{iso_n} = 10⁸ Ohm
• R_{mess_p} = R_{mess_n} = 2*10⁶ Ohm
• Frequenz f = 1/20 Hz
• Spannung U = 800 V
• R_VP = U*U/1000
• R_VN = U*U/1000

The following simulation parameters were used:

• R _{iso_p} = 10 ⁸ ohms
• R _{iso_n} = 10 ⁸ ohms
• R _{meas_p} = R _{meas_n} = 2*10 ⁶ ohms
• Frequency f = 1/20 Hz
• Voltage U = 800 V
• _RVP = U*U/1000
• _RVN = U*U/1000

9 shows schematic diagrams for the representation of switching positions U _S1 , U _S2 of the switches S1 , S2 , the potentials H+ , H- and the calculated insulation resistances R _{iso_P} , R _{iso_N} over time t for a simulation without the coupling resistance R _K .

Due to the well-insulated HV vehicle electrical system 1, the insulation monitor 5, in particular a resistance insulation monitor, causes a significant shift in the potentials H+, H-. The Y capacitances C _{Y_P} , C _{Y_N} thus assume a voltage which almost corresponds to the voltage of the HV battery 2 . Their energy content is therefore very high. The charge reversal time is very slow due to the high-impedance resistors and the charge reversal is not yet complete in the cycle time of the insulation monitor 5 in this example.

10 shows schematic diagrams for representing switching positions U _S1 , U _S2 of switches S1, S2, the potentials H+, H- and the calculated insulation resistances R _{iso_P} , R _{iso_N} over time t for a simulation with a coupling resistance R _K of 10 ⁶ ohms.

The simulation makes it clear that the potentials H+, H- fluctuate less than in a system without a coupling resistor R _K at the voltage center tap 6. The maximum potential H+, H- is 531 V, the minimum potential H+, H- is 269 V. The energy contents in the Y-capacitors C _{Y_P} , C _{Y_N} are thus significantly reduced. Because of the relatively low coupling resistance R _K compared to the insulation resistances R _{iso_P} , R _{iso_N} , the charge reversal can take place much more quickly. The insulation monitor 5 can therefore detect insulation faults in a shorter time.

Reference List

1

electrical system

2

HV battery

2.1,2.2

HV battery

3

HV consumer

4

HV consumer

5

isolation guard

6

Voltage center tap

7

Three-phase AC connection

8th

rectifier

9

DC charging station

11

3 level DC boost converter

12

Ground cable

13

H bridge

14

H bridge

15

3 level inverter

16

electric machine

17

B& Bridge Inverter

C

output capacity

Cx_P, Cx_N

capacity

CY_P, CY_N

Y capacity

Cy_P1, CY_N1

Y capacity

H+, H-

potential

PA

vehicle mass

PA'

Dimensions

RF

fixed resistor

Riso_P, Riso_N

insulation resistance

RK

coupling resistance

RL

line resistance

Rmess_p, Rmess_n

measuring resistor

rev

variable resistance

RVP, RVN

consumer resistance

Riso_P1, Riso_N1

insulation resistance

S1, S2

Switch

t

Time

US1, US2

switching position

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102019202892 A1 [0002]

Claims (10)

Vehicle electrical system (1) for a motor vehicle, comprising at least one HV battery (2) for providing a positive potential (H+) and a negative potential (H-) and at least one HV consumer (3, 4), with an insulation monitor (5 ) for monitoring insulation resistances (R _{iso_P} , R _{iso_N} ) to a vehicle ground (PA) that is galvanically isolated from the vehicle electrical system (1), with between the positive potential (H+) and the vehicle ground (PA) and between the negative potential (H- ) and the vehicle ground (PA) each have a Y-capacitance (C _{Y_P} , C _{Y_N} ), characterized in that a voltage center tap (6) present in the vehicle electrical system (1) or in a component of the vehicle electrical system (1) between the positive potential (H+) and the negative potential (H-) is connected to the vehicle ground (PA) by means of an ohmic coupling resistor (R _K ). electrical system (1) according to claim 1 , characterized in that the voltage center tap (6) is between two resistors connected as a voltage divider or is formed by a capacitive voltage divider. on-board network claim 2 , characterized in that the resistances of the voltage divider are designed as HV consumers (3, 4) connected in series or as internal resistances of at least two HV batteries (2.1, 2.2) connected in series. electrical system (1) according to claim 3 , characterized in that the resistances of the voltage divider are significantly smaller in comparison to the coupling resistance (R _K ) and to measuring resistances (R _{mess_p} , R _{mess_n} ) of the insulation monitor (5), which is designed as a resistance insulation monitor. electrical system (1) according to claim 4 , characterized in that the measuring resistors (R _{mess_p} , R _{mess_n} ) and the coupling resistor (R _K ) are in the range of more than 100 kOhm. Vehicle electrical system (1) according to one of the preceding claims, characterized in that the coupling resistor (R _K ) comprises a fixed resistor (R _F ) and/or a variable resistor (Rv). electrical system (1) according to claim 6 , characterized in that the coupling resistor (R _K ) is designed as a series connection of the fixed resistor (R _F ) and the variable resistor (Rv). Vehicle electrical system (1) according to one of the preceding claims, characterized in that at least one from the following list is coupled to the vehicle ground (PA) via the coupling resistor (R _K ): - a series connection of HV voltage supplies for control boards, - a series connection of Half-bridges and/or H-bridges, - a multi-level half-bridge, - a series connection of inverters, - a multi-level inverter, - a heating circuit with series connections of two or more heating elements, - a tap of a connection point of battery module series connections. Vehicle comprising an on-board network (1) according to one of the preceding claims. Method for operating a vehicle according to claim 9 , characterized in that the coupling resistor (R _K ) is designed as a series connection of the fixed resistor (R _F ) and the variable resistor (Rv), wherein when the vehicle is not connected to a DC charging station, a high variable resistor ( Rv) is set, with a lower variable resistance (Rv) being set when the vehicle is connected to a DC charging station.

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